Figure 20-3 describes the software and hardware operations involved
in
a typical transmit operation.
Protocol
Transmit
Stack
13(
) 1
Packet.
The numbered steps are described as follows:
Buffer Descriptor Table
1.
The protocol stack (high-level software layer) initiates a packet transmit.
Buffers
2.
Software device driver parses the protocol stack buffer into descriptor table entries and buffers.
3.
Software device driver instructs the GOMMAG to process a new transmit packet.
4.
The GOMMAG channel requests
MAL
to process a new packet.
5.
MAL fetches descriptor information.
6.
MAL writes control information into the GOMMAG and initiates the data move.
7.
Packet data is transferred from memory into the GOMMAG (the GOMMAG controls the pace
of
the
data transfer).
8.
The packet is transmitted on the media (steps 7 and 8 can overlap).
9.
The GOMMAG requests that
MAL
read the packet status.
10. The status read by
MAL
is written back into a buffer descriptor.
11. Software is interrupted (if interrupt conditions are met) by the
GOMMAG or by the
MAL
end-of-buffer
interrupt.
12. Software clears the interrupt status bits
in
the GOMMAG and in MAL.
13. Software informs the protocol stack that transmission is complete.
Figure 20-3. Transmit Operation
Preliminary
Memory Access Layer
20-5
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